Kinetic study of Nafion degradation by Fenton reaction

To predict the durability of polymer electrolyte membranes in fuel cells, the degradation reactions of Nafion 117 films were studied as oxidation reactions with hydroxyl radicals as oxidation accelerators. The radical species were generated by the Fenton reaction between hydrogen peroxide (H2O2) and iron ions (Fe2+). The Nation degradation kinetics were estimated by fluorine ion (F-) generation. The H2O2 and Nafion degradation reactions fit a pseudo-first-order rate constant. The values of the activation energy and frequency factor are 85 kJ mol(-1) and 3.97 x 10(8) s(-1) for H2O2 decomposition in the presence of a Nafion film and 97 kJ mol(-1) and 9.88 x 10(8) s(-1) for F- generation. The Nation surface morphology became rough after reaction for 12 h; small cracks, approximately 100 mu m in length, were observed at temperatures below 60 degrees C. These cracks connected to make larger gaps of approximately 1 mm at temperatures above 70 degrees C. We also found a linear relationship between H2O2 consumption and F- generation. The rate constant is temperature dependent and expressed as In(d[F-]/d[decomposed H2O2])=-19.5 x 10(3) K-1 + 42.8. F- generated and H2O2 consumed along with the Nation degradation conditions can be predicted using this relation. (C) 2010 Elsevier B.V. All rights reserved.